Timezone to use for Google Business Messaging

What timezone should I be using for Google Business Messages?

I am using this excellent guide: Google Business Messages (GBM) | yellow.ai

However the timezone options in the two TZ fields on the second menu of building out the bot are all numeric 0-541. I have tried a few numeric options here & keep getting an error so am unable to proceed.

Hey Yellow.AI team, can anyone assist with this one? If not, how do I log a ticket?